TwoDee is my level editor for 2D games. It was initially intended for non-tile-based games, and dealing with collision edges for use by physics engines – specifically for ‘Fluff’. But it has also been adapted to support tilemaps (for Little Acorns).
The editor is a C#/WinForms/SlimDX app, and level data is exported as XML. I’ll write a bit more about the editor one day…
The TwoDee editor, editing a level for the Fluff prototype